1. Field of the Invention
This invention relates to a heater which will be effective if used in a fixing device for heating and fixing a toner image formed on a recording material, and an image heating apparatus using this heater.
2. Related Background Art
An image heating fixing apparatus for heat fixing of a toner image formed on a recording material is described below as an example of an image heating apparatus.
In an image forming apparatus such as a copier, printer, or facsimile, an image heating fixing apparatus is a heating apparatus for heating/fixing-processing, on a recording material surface, an unfixed toner image corresponding to image information formed on the surface of a recording material (electro fax sheet, electrostatic recording sheet, transferring material sheet, print paper, or the like) in a direct or indirect (transferring) system using toner made of a thermomeltable resin or the like by proper image forming process means such as electrophotography, electrostatic recording, magnetic recording, or the like.
Conventionally, for such an image heating fixing apparatus, a heat roller system has been widely used. The heat roller system is a system which has a basic construction comprising a metallic roller provided therein with a heater, and a pressure roller having an elasticity and pressure-contacted to said roller, and in which, by passing a recording material through a fixing nip portion formed by one pair of these rollers, an unfixed toner image bore on said recording material is heated and pressurized to fix.
However, in the above heat roller system, since the heat capacity of the roller is large, very much time was required for raising the roller surface to a desired fixing temperature. Besides, for this reason, for quickly executing an image output operation, there is a problem wherein the roller surface must be temperature-adjusted to a temperature in a certain extent even when a machine is not used.
One improved and devised on that point is disclosed in Japanese Patent Application Laid-open No. 10-293490. This is composed by an insulating layer and a heat generation layer are laminated on a surface of a metallic roller. Such a roller is difficult in manufacture, besides, since a contact point for supplying an electric power to the roller slides, problems such as generation of noise and a short duration arise, so it does not reach a practical use in practice.
So, the present applicant has proposed before a heating apparatus of a film heating system (for example, see Japanese Patent Application Laid-open No. 63-313182, Japanese Patent Application Laid-open No. 2-157878, Japanese Patent Application Laid-open No. 4-44075, and Japanese Patent Application Laid-open No. 4-204980. 
This film heating system is a system in which a heater and a material to be heated are respectively put on one surface side and the other surface side of a heat-resisting film so as to give the thermal energy of the heating body to the heated material through the heat-resisting film, and a heating apparatus of an on-demand type in which members of low heat capacity can be used for the heating body and film, there is quick startability, and the power consumption in standby is considerably small, can be constructed.
FIGS. 7A to 7C show one example of a heating apparatus of the film heating system. This example is an image heating fixing apparatus of the film heating system. FIG. 7A is an enlarged cross-section model view of a principal part, FIG. 7B is a partially cut-off plan model view on the surface side of a heating body, and FIG. 7C is a plan model view on the back surface side of the heating body.
Reference numeral 7 denotes a heater, which is a slender and thin-plate-shaped member whose longitude is a vertical direction to the drawing surface of FIG. 7A, entirely low heat capacitive, and generates heat by being electrified.
Reference numeral 13 denotes a heater support member, whose longitude corresponds to a vertical direction to a drawing surface of FIG. 7A, being adiabatic and rigid. On the lower surface side of this support member 13, along the member longitude, a seat gouged portion 13a elongating in the longitudinal axis and in shallow grooved shape into which the above heater 7 can be fitted is comprised, and the heater 7 is fitted into this seat gouged portion 13a and supported by the support member 13.
Reference numeral 12 denotes a thin heat-resisting film and reference numeral 9 denotes an elastic pressure roller. The film 12 is put between the heater 7 supported by the support member 13 and the pressure roller 9 so that a fixing nip portion (heating nip portion) N is formed by contacting and providing a predetermined pressure force with each other.
The film 12 moves in an arrow direction with close contacting the fixing nip portion N to the surface on the downward facing side of the heater 7 and sliding by a not-shown drive member, or the pressure roller 9 being rotation-driven.
And, when a paper leaf body (recording material) 11 carrying an unfixed toner image 10, as a heated material, is introduced between the film 12 of the above fixing nip portion N and the pressure roller 9, the paper leaf body 11 is sandwich-conveyed in the fixing nip portion N together with the film 12 and heated by heat from the heater 7 through the film 12, and unfixed toner 10 is heat-fixed on the paper leaf body surface. The paper leaf body 11 passed through the fixing nip portion N is separated from the surface of the film 12 and conveyed.
Generally, a ceramic heater in which a ceramic board a heating body board having electrical-insulating performance, good heat conductivity and heat-resistivity is used as the heater 7. In this embodiment, a ceramic heater is also used as the heater 7.
That is, numeral 1 denotes a slender and thin-plate-shaped ceramic board.
Reference numeral 2 denotes first and second parallel two-stripe narrow-band-shape electrification heat-generation resistor patterns (one is a first, the other is a second) formed and comprised along the board longitude on the surface side of this ceramic board 1.
Reference numeral 5 denotes two conductor patterns (one is a first, the other is a second) as the first and second power supply electrodes (electrode contact points) formed and comprised with being arranged on the longitude one end portion side of the ceramic board surface. The first power supply electrode 5 is electrically conducted to one end portion of the first resistor pattern 2 through an extension pattern portion. Besides, the second power supply electrode 5 is electrically conducted to one end portion of the second resistor pattern 2 through an extension pattern portion.
Reference numeral 6 denotes a conductor pattern as a folded-back electrode formed and comprised on the ceramic board surface by electrically conducting between the other end portions of the first and second resistor patterns 2.
Reference numeral 3 denotes a heater surface protective glass layer, which is formed and comprised to cover substantially entirely the heater surface except the portion of the first and second power supply electrodes 5. By this protective glass layer 3, each extension pattern portion of the first and second resistor patterns 2 and the first and second power supply electrodes 5, and the folded-back electrode 6 are protected by being covered.
Reference numeral 4 denotes a temperature sensing element such as a thermistor or the like, which is disposed by being contacted to substantially the center portion in the longitudinal direction on the heater back surface side, that is, the back surface side of the ceramic board 1.
The surface side having the surface protective glass layer 3 of the above ceramic heater 7 is the film sliding surface side, and the surface side of this ceramic heater 7 is exposed to the exterior and fitted in the seat gouged portion 13a on the lower surface side of said support member 13 and disposed.
Reference numeral 8 denotes a power supply connecter. By predetermined fitness to the power supply connecter mounting portion of the support member 13 disposing and supporting the heater 7, first and second power supply spring contact points 8a on the power supply connecter 8 side are pressurized and contacted to the first and second power supply electrodes 5 of the heater 7, and the heater 7 and a not-shown power supply circuit are electrically connected.
By performing power supply from the power supply circuit through the power supply connecter 8 to the first and second power supply electrodes 5, by the electrification heat-generation resistor patterns 2 generating heat throughout the longitude entire length, the heater 7 rapidly raises the temperature. And, the temperature rising information is converted into voltage information by the temperature sensing element 7 disposed on the heater back surface side and detected, the output is calculated by a not-shown control circuit such as CPU or the like, and an AC input from the power supply circuit to the heater 7 is adjusted so that the temperature of the heater 7 is temperature-controlled to a predetermined temperature.
In the fixing apparatus adopting such a film heating system, since the film 12 of a low heat capacity and the heater 7 can be used, it becomes possible to shorten a wait time (quick start) as compared with the conventional heat roller system. Besides, since the quick start can be done, pre-heating upon non-print operation becomes unnecessary, and power-saving in a synthetic meaning can be intended.
By the way, as the ceramic heater of the above-described example, the heating body using the ceramic board such as alumina as the board has the problems that the ceramic is fragile, or, the cost is high, it is unsuitable for bending processing or the like, and the like.
So, in Japanese Patent Application Laid-open No. 9-244442, Japanese Patent Application Laid-open No. 10-275671, a heating body (hereinafter, referred to as conductive board heater) in which, by forming an insulating layer on a metal, a board having the same insulation ability as the conventional ceramic board is made, and a resistor pattern, a conductor pattern, and an insulating sliding layer of the uppermost layer are formed thereon is proposed.
Now, as a countermeasure in which the heater is out of control, i.e., a safety countermeasure for the excessive temperature rise of the heater due to the occurrence of the situation in which the supply of electric power to the heater does not stop and the heater continues to generate heat when a temperature detecting element goes wrong or a control device goes wrong, there is a construction which is provided with a safety countermeasure element such as a thermoswitch or a temperature fuse and in which during the no thermal control of the heater, the power supply circuit to the heater is urgently cut off by the operation of the safety countermeasure element.
In addition, when the heater is a heater using a ceramic board such as alumina, the ceramic board cannot stand thermal stress against the excessive temperature rise of the heater during the no thermal control and causes crack, and with this crack of the board, a resistive element pattern and a conductor pattern are also broken (the self-breakage of the heater when the heater is out of control) and at that point of time, the supply of electric power to the heater stops, and this becomes a dual safety countermeasure.
In the case that a conductive board heater is used, however, the cut-off of the supply of electric power to the heater by the crack of the board when the heater is out of control could not be expected.
The present invention has been made in view of the above-noted problem and an object thereof is to provide a heater which is high in safety and an image heating apparatus using this heater.
Another object of the present invention is to provide a heater contrived so that a heat generating resistive element may be self-broken when the heater has abnormally risen in temperature and an image heating apparatus using this heater.
Still another object of the present invention is to provide a heater comprising:
an electrically conductive substrate;
a first electrically insulating layer formed on the electrically conductive substrate;
a heat generating resistor formed on the first electrically insulating layer; and
a second electrically insulating layer formed on the heat generating resistor;
wherein when the glass transition temperature of the first electrically insulating layer is defined as T1 and the glass transition temperature of the heat generating resistor is defined as T2 and the glass transition temperature of the second electrically insulating layer is defined as T3, T1, T2 and T3 have the relation that T1 greater than T3xe2x89xa7T2 or T1 greater than T2xe2x89xa7T3.
Yet still another object of the present invention is to provide an image heating apparatus comprising:
a heater comprising an electrically conductive substrate, a first electrically insulating layer formed on the electrically conductive substrate, a heat generating resistor formed on the first electrically insulating layer, and a second electrically insulating layer formed on the heat generating resistor;
wherein when the glass transition temperature of the first electrically insulating layer is defined as T1 and the glass transition temperature of the heat generating resistor is defined as T2 and the glass transition temperature of the second electrically insulating layer is defined as T3, T1, T2 and T3 have the relation that T1 greater than T3xe2x89xa7T2 or T1 greater than Txe2x89xa7T3; and
a backup member for forming nip cooperation with the heater.
Further objects of the present invention will become apparent from the following detailed description when read with reference to the accompanying drawings.